This research is designed to investigate the effects of protein-rich diets on calcium status and bone metabolism in young, aging and aged animals. The proposed research will involve the feeding of normal and high levels of dietary protein combined with deficient, normal and high levels of dietary calcium. Calcium absorption and retention will be monitored by balance methods; further information relative to calcium absorption will be obtained by in vitro measurements of calcium metabolism in the intestinal mucosa. The effects of high protein and ranging calcium intakes on alterations in bone metabolism will be assessed by chemical and histological examination and by measurements of mechanical strength properties of femur. Study of the interrelationships of high protein diets and calcium status and changes in bone properties in aging is of interest not only from a general gerontological viewpoint but also because of its relevance in the etiology of senile osteoporosis.